(1) Field of the Invention
The present invention relates to a water base ink composition, more specifically to a water base ink composition for an ink jet-recording apparatus capable of being used in an ink jet system recording apparatus which is commercially available, and a water base ink composition for writing instruments which is not blurred in writing and is useful for writing instruments such as a sign pen and a ball point pen.
(2) Description of the Prior Art
Ink compositions comprising water soluble acidic dyes or basic dyes dissolved in water base media and additives such as humidifiers, pH controllers and preservatives are known as conventional ink compositions for ink jet-recording apparatuses.
However, these ink compositions have the defects that the printed parts are blurred and the images become unclear and that since the dyes are water soluble, the recorded images are blurred or disappear with sweat and water or the colors become turbid by color mixing. Originally, water soluble dyes are inferior in light fastness and have the problem that preservation of the printed matters over a long period of time causes the images to deteriorate. Further, these ink compositions have the defects that preservation thereof over a long period of time and repeated printing cause a change in the physical properties of the inks and produce precipitates, so that nozzles are clogged or cause marked troubles in discharging to bring about inferior printing.
Dyes and pigments have so far been known as coloring components for water base inks used for writing instruments such as water base sign pens and water base ball point pens.
Inks using dyes have the defect that since the dyes are water soluble, the written characters and the drawn lines are blurred or disappear with sweat and water, so that the written characters and the drawn lines become unclear. Thus, the inks are inferior in so-called water resistance. Further, there is the problem that the dyes themselves are inferior in light fastness, so that the written characters and the drawn lines deteriorate during a long period of time.
On the other hand, inks using pigments have no problems on water resistance and light fastness but the pigments are flocculated and precipitated during a long period of time to bring about the problems such as clogging at pen points and inferior writing. In inks for writing instruments, the pigments are required to be finely dispersed, and therefore it is difficult to disperse various organic pigments to increase the color number of the inks.